GB2027714A - Process and Apparatus for the Manufacture of Swellable Crosslinked Carboxyalkylcelluloses From Natural Cellulose or Cellulose Hydrate and Use Thereof - Google Patents

Abstract

A process for the manufacture of a swellable crosslinked carboxyalkylcellulose by treating cellulose or cellulose hydrate fibres or sheet with etherifying and crosslinking agents in an aqueous alkaline medium in excess, removing the excess and heating. The process may be carried out in apparatus comprising a reaction medium mixing and storage tank (6), a sieve drum washer (2) in which the reaction medium is contacted with the cellulose material, a padder (3) in which the excess medium is removed, and finally a heated sieve drum drier (5) or a sieve belt steamer (2). <IMAGE>

Description

SPECIFICATION Process and Apparatus for the Manufacture of Swellable Crosslinked Carboxyalkylcelluloses from Natural Cellulose or Cellulose Hydrate and Use Thereof This invention relates to a process for preparing swellable crosslinked carboxyalkyl celluloses from natural cellulose or cellulose hydrate, to apparatus, for carrying out such a process, and to the use of the products especially in nonwoven fabrics.

Recently, swellable carbohydrate derivatives, for example, swellable crosslinked cellulose ethers, particularly carboxyalkylcelluloses, have gained increasing significance in all fields in which physiological fluids, for example, urine, blood, perspiration, and saliva, must be absorbed, namely in infant care, feminine hygiene, and in medical practices and hospitals. They are used as the sole components of, or additives to cellulose in the absorptive compositions used, e.g., in tampons, sanitary pads, nonwoven fabrics of other sorts, nappies, or under-blankets.

Further, these swellable substances are used to improve the ability to absorb water vapour of bonded nonwoven fabrics which have many uses. These uses include the replacement of leather or other textiles in, for example, shoes (shoe uppers, linings, soles), bags, upholstery covers, outer garments ("leather" and all-weather garments) or textiles and articles for domestic use (table cloths, window "leathers", wiping cloths). The substances are, however, also used in combination with or as complements to the materials (e.g. leather or textiles) which may be employed for the above mentioned purposes, apart from the nonwoven fabrics.

Other uses for the swellable substances are in sheet materials capable of absorbing and transmitting water vapour and prepared from various natural or synthetic polymers, for example, polyvinyl chloride, polyurethane, rubber, polyalkylenes (poly olefins), and cellulose hydrate. These sheet materials which may be, for example, self-supporting films or coatings on substrates are particularly suitable as leather substitutes (synthetic leather) for use in shoe uppers, upholstery covers, bags, and outer garments ("leather" and all-weather garments), or as covering materials, e.g., tent materials or tarpaulins.

Various processes have been proposed for preparing swellable carbohydrate derivatives, e.g., swellable cross-linked cellulose ethers. Publications describing them include: German Offenlegungsschrift 1,912,740 (British Specification No. 1,236,313) (United States Patent, 3,589,364), which describes carboxymethyl-cellulose fibres which are substantially insoluble in water, and which are suitable for absorbing and retaining aqueous solutions. They are wet-crosslinked fibres of originally water-soluble salts of carboxymethylcellulose (CMC) having a degree of substitution (DS) of about 0.4 to 1.6, which retain the original structure of the cellulose fibres.They are either prepared in a single reaction step in which the cellulose is simultaneously carboxymethylated and wet crosslinked or in two reaction steps in which the cellulose is first wet-crosslinked and then carboxymethylated. The starting material for the process is natural or regenerated cellulose; the crosslinking agent is caused to act under alkaline or acid conditions. Among the various crosslinking agents epichlorohydrin is preferred. The cellulose fibres are suspended in an inert organic diluent, for example, isopropanol, in the presence of a small amount of water, and are treated under alkaline conditions with about 3 to 10% by weight of the crosslinking agent. The amount of the inert organic diluent used corresponds to about 40 times the amount of cellulose.

German Offenlegungsschrift 2,364,628 (British Patent Specification No. 1 ,492,040) discloses a hydrophilic structure, of a fibre-forming and a film-forming water-insoluble polymer, which contains particles of modified cellulose ethers which are treated to the extent that, if etherification only were carried out, water-soluble cellulose ethers would result, but which are modified in such a way that they are at least predominantly water-insoluble while retaining the capacity to absorb water. The structures are preferably films but may also be filaments, provided they are prepared in a usual precipitation process, e.g., from regenerated cellulose. The pulverulent or granular material composed of the modified cellulose ethers is, for example, added to the polymer composition and is uniformly distributed therein prior to forming.

A process for improving the absorption of water and the absorptivity of fibre materials composed of or containing synthetic fibres or filaments is described in German Offenlegungsschrift 2,441,781. In this process, modified highly-absorbent cellulose ethers are fixed to the fibre materials with the aid of finishing agents, permanent-finishing agents, resins, or binders. The modified cellulose ethers are, together with the agents serving to fix them to the fibre material, applied from aqueous preparations, such as solutions, dispersions, or emulsions. A cellulose ether modified with N-methylol acrylamide is preferably used, in an amount of about 0.1 to 5% relative to the weight of the improved fibre material.

In the process for the preparation of highly-absorbent cellulose filaments of German Offenlegungsschrift 2,447,282 (corresponding to United States Patent 3,997,647) modified cellulose fibres are caused to swell in a liquid, so that they can be extruded in the swollen condition; during extrusion the fibres are oriented, and they combine to form filaments. The filaments are then dried to reduce the swelling of the fibres and to allow the formation of capillary-like longitudinal channels within the filaments. By "modification of the cellulose" a chemical substitution, a chemical substitution and crosslinking, or a graft-polymerization is to be understood.

German Offenlegungsschrift 2,519,927 (United States Patent 4,068,068) (British Patent Application 17919/76, Serial No. 1552851) discloses a process for the preparation of cellulose ethers which absorb water, but are to a large extent insoluble in water. In this process, cellulose is treated in the presence of an alkali with an etherifying agent in such a way that a water-soluble cellulose ether would result, if only etherification were carried out. Prior to, simultaneously with, or after etherification of the cellulose crosslinking with bisacrylamido-acetic acid is effected.The cellulose is alkalized in a first step, and in a second, if necessary in a third step, the other reaction components are, successively or together, added to the alkalicellulose in the presence of 0.8 to 7.5 parts by weight of isopropanol, relative to the weight of the cellulose, and are caused to react for about 1 hour at a temperature of about 50 to 800C. The last-mentioned reaction may also be performed directly with the alkali-cellulose which is moist with water, without the addition of isopropanol, provided the existing mixture of powder or crumbs is loose and does not stick together.

A similar way of carrying out the reaction without any organic diluent has also been disclosed in German Offenlegungsschrift 2,520,337 (British Patent Application No. 18473/76, Serial No. 1 552861 United States Patent 4,066,828). The crosslinking agents used are acrylamidomethylene chloroacetamide, dichloroacetic acid, phosphorus oxychloride, or compounds of a kind, which are reactive towards cellulose in alkaline media, and contain at least two acrylamido groups, chloroazomethine groups, or allyloxyazomethine groups.

German Offenlegungsschrift 2,543,1 87 (British Patent Application No. 39754/76, Serial No.

) describes another method of effecting the reaction without any organic diluent. In this method, clippings from lacquered or unlacquered cellulose hydrate films are alkalized in a first step, and are then etherified using a halogen-containing fatty acid, for example, monochloro-acetic acid, and reacted with a polyfunctional crosslinking agent.

German Offenlegungsschrift 2,710,874 (British PatentApplication No. 9568/78) describes a process in which rayon staple fibres are placed in a reactor equipped with a pump circulating system for solvents and are alkalized with an about 50% strength aqueous NaOH solution, in the presence of about 13 parts by weight of a 87% strength isopropanol per part by weight of fibres. Then the alkaiized rayon staple fibres are etherified with Na-monochloroacetate and simultaneously crosslinked with bisacrylamido-acetic acid for about 1 hour at a temperature of about 700 C. Upon completion of the reaction the mixture is neutralized and filtered, and the solid residue composed of crosslinked etherified rayon staple fibres is washed free from salt in an aqueous alcohol.The fibre material obtained has a good absorption and retention capacity for water is water-insoluble to the extent of about 70%.

The previously proposed processes have, however, various disadvantages: In all the preparation processes, alkalizing is carried out separately, which is time-consuming, prior to the etherifying and/or crosslinking reaction.

The more or less important quantities of organic diluents used require expensive special apparatus in order to recover these diluents or to reprocess them in an ecologically acceptable way, and also to meet the stringent requirements with respect to the operational safety of the processes in which these diluents are employed.

In the processes which are carried out without adding any organic diluents the course of the reaction is often very irregular, because the mixture of powder or crumbs used makes it difficult for the reaction components to reach all reactive areas of the cellulosic material.

The application of absorbent modified cellulose ethers or similar substances to the surfaces of fibres, or the incorporation of these substances in the raw material used for preparing the fibres, often renders difficult further processing. In addition, it is inconvenient that the absorbing capacity of the modified cellulose ethers added is reduced either by the auxiliary agents used to facilitate the application, or during the fibre production from the component mixture.

The preparation of fibres and/or filaments directly from modified cellulose derivatives can normaily only be carried out using cellulose derivatives which are not too highly swellable, because otherwise fibre and/or filament production is rendered difficult by the swelling liquids.

There still remains a need for a process and apparatus for preparing crosslinked carboxyalkylcelluloses which do not require a great number of expensive apparatus and provide shaped structures, especially fibres, textile sheet materials containing these fibres, or sheet materials of other kinds, which are based on natural cellulose or cellulose hydrate and exhibit a good swelling capacity.

The present invention provides a process for the manufacture of a swellable crosslinked carboxyalkylceilulose which comprises treating a shaped structure comprising cellulose hydrate or natural cellulose with an aqueous alkaline medium containing a carboxylating etherifying agent and a crosslinking agent, the quantity of the medium and the reactants contained therein being greater than required for reaction with the cellulose or cellulose hydrate, then removing part of the medium, while leaving sufficient for the reaction, and heating the cellulose or cellulose hydrate and the remaining reaction mixture.

Advantageously, the shaped structure is or shaped structures are fibres, textile sheet material containing fibres, or sheet material of other kinds, based on cellulose hydrate or natural cellulose.

The present invention also provides swellable crosslinked carboxyalkylcellulose made by the process of the invention.

Swellable carboxyalkylcelluloses are those which swell when they are immersed in aqueous liquids, particularly liquids containing more than 50% by weight of water, or when they come, in another way, into contact with water molecules (for example water vapour); they are water-insoluble to the extent of at least 30% by weight, advantageously, at least 50% by weight. The carboxyalkylcelluloses prepared according to the present invention are advantageously either in the form of fibres having lengths of 0.1 mm to 200 mm, preferably of 1 mm to 150 mm, if a fibriform starting material is used, or in the form of sheet materials, if the starting material is a film or a sponge cloth, and they will be referred to as fibres and sheet for convenience.

The process of the invention is, advantageously, carried out in such a way that fibres of natural cellulose or of cellulose hydrate or sheet materials containing these fibres, are sprayed with or immersed in the aqueous alkaline reaction mixture which contains the aqueous solution of an alkalizing agent, the carboxyalkylating etherifying agent, and the crosslinking agent. This process step is, among others, carried out to achieve a good mixture, because producing a uniform contact between the fibres or the sheet materials and the other reaction components will yield the advantage of a uniform course of the reaction, i.e., an as far as possible homogeneous substitution on the cellulose molecules can be obtained.

For the purpose of the actual chemical reaction the surplus quantity of the reaction mixture is removed again from the material. This may, particularly, be done by squeezing off or centrifuging. The surplus quantity removed is at most the quantity which is not required for the chemical reaction of the cellulose with the aqueous mixture composed of the alkalizing, etherifying, and crosslinking agents; appropriately it amounts to a multiple of the quantity which is actually needed for the reaction, for example, 5 to 50 times the quantity. To effect the chemical reaction the mixture composed of the fibres or sheet materials and the remainder of the reaction mixture is treated with heat energy.Heat energy is appropriately applied in the form of hot air, for example, in a drying apparatus (e.g. a drying chamber) equipped with an air circulating system, or in another type of equipment in which hot air or superheated steam streams through the material to be treated; or heat energy is generated by means of microwaves. If microwaves are employed, heat is not applied from the outside, as in the case of the other process variants mentioned, but is generated directly in the fibres or sheet materials, i.e. at the place of the actual chemical reaction.

The required reaction times depend, inter alia, Upon the transmission of heat through the fibres or sheet materials, and accordingly the better the heat transfer, the shorter the reaction time. The advantageous reaction time ranges between 1 5 seconds and 60 minutes, depending upon the way in which heat energy is supplied. If hot air or superheated steam is used the reaction time ranges, for example, preferably from 1 minute to 10 minutes, at a temperature of the hot air of about 700C to about 1 600 C. If, on the other hand, microwaves are employed the reaction time advantageously ranges from 1 5 seconds to 60 seconds.

For economical reasons, an aqueous NaOH solution is nearly always used as the alkalizing agent for the natural cellulose or the cellulose hydrate when carrying out the process of the invention. Other aqueous alkaline solutions, for example, KOH or LiOH solutions, are, however, also suitable as alkalizing agents. The concentrations of the aqueous solutions may vary within wide limits, appropriately they range from 10 to 60% by weight.

As the carboxyalkylating etherifying agents monochloroacetic acid or the salts thereof are preferred; but monochloropropionic acid or acrylamide may also be used, and then the carboxyalkylation is a carboxyethylation, or preferably, a carboxymethylation and results in a carboxymethyl cellulose (CMC) or a carboxyethyl cellulose (CEC). If the process of the invention were carried out without crosslinking, the degree of substitution (DS) of the resulting cellulose ethers would be such that the latter would be at least partially water-soluble.

As well as etherification, crosslinking takes place in the process according to the invention, and crosslinking results in products which absorb comparatively large quantities of water and are also capable of retaining these quantities more or less well, without dissolving completely themselves. The crosslinking agents mentioned below are preferred for this purpose; of these particularly, 0.0005 to 0.2 part by weight must in general be used, relative to 1 part by weight of the natural cellulose or the cellulose hydrate.They are compounds carrying at least one of the following funtional groups reactive towards hydroxyl groups: the acrylamido group, R1 being H or CH3

an a halogenoepoxy group, Hal being Cl or Br

the chloroazomethine group

the allyloxy-azomethine group

The crosslinking agent may alternatively be phosphorus oxychloride or acrylamido-methylene chloroacetamide. Dichloro-acetic acid which may also be employed as a crosslinking agent must, however, in general be used in a quantity of at least 0.01 part by weight per part by weight of the natural cellulose or of the cellulose hydrate.

The following are examples of compounds carrying the functional groups mentioned: methylene bisacrylamide, bisacrylamido-acetic acid, N,N'-dimethylol methylene bisacrylamide, 1,1 -bisacrylamidoethane, methylene bismethacrylamide, epichlorohydrin, 2,4,6-trichloropyrimidine, 2,4,5,6-tetrachloropyrimidine, cyanuric chloride, triallyl cyanurate.

The cellulosic starting materials used in the process of the invention may be, on the one hand, composed of fibres of a natural cellulose, which are, for example, prepared from the fibrocellules of more highly developed plants, e,g., from cotton, bast, leaf, wood, and grass fibres (e.g. cereal straw, bamboo, sugar cane waste), including, among others, raw cotton, cotton linters, pulp, ramie, flax, or hemp. The natural-cellulose fibres may, however, also be in the form of a finished textile sheet material, for example, a woven or a nonwoven fabric, in which these fibres may constitute the whole of the fabric or may be blended with other fibres, for example, fibres of cellulose hydrate or synthetic fibres, such as polyester fibres.

On the other hand, the cellulose starting materials used may be fibres or sheet materials, such as films or sponge cloths, of cellulose hydrate, i.e., fibres, films or sponge cloths of regenerated cellulose (for example, viscose, i.e., fibres, films or sponge cloths prepared from cellulose sodium xanthogenate in precipitating baths). Preferably, so-called rayon staple fibres are used, i.e. fibres of cellulose hydrate which have been cut as uniformly as possible and have lengths ranging from about 30 to about 1 50 mm, particularly from about 30 to about 60 mm.The cellulose hydrate fibres may, however, also be in the form of a finished textile sheet material, for example, a woven or a nonwoven fabric, in which these fibres may constitute the whole of the fabric or may be blended with other fibres, for example, fibres of a natural cellulose, such as cotton, or synthetic fibres, such as polyester fibres.

Advantageously, the molar relationships of the components to be used in the process according to the invention i.e., after the removal of surplus reaction medium, range from 0.7 to 2.1 moles of alkali hydroxide, 10 to 30 moles of H20, 0.7 to 2 moles of the etherifying agent, and 0.005 to 0.1 mole of the crosslinking agent (relative to 1 mole of cellulose).

The invention also provides apparatus for carrying out the process for preparing swellable crosslinked carboxyalkylcellulose by reacting cellulose, a carboxyalkyiating etherifying agent and a crosslinking agent in an aqueous alkaline medium, which comprises: a) a unit for preparing and storing the aqueous alkaline reaction medium containing the etherifying and crosslinking agents (hereinafter termed the reaction mixture), b) a unit for contacting fibres, textile sheet materials containing these fibres, or sheet materials of other kinds having a basis of cellulose hydrate or of natural cellulose with an ample quantity of the reaction mixture, c) a unit for removing the reaction mixture from the fibres or sheet materials contacted therewith, so that at least the quantity required for reaction is still present, d) a unit for treating with heat energy the fibres or sheet materials containing the remainder of the reaction mixture, and connecting elements between units a to d.

In the apparatus according to the invention the process of the invention may either be performed discontinuously or, advantageously continuously, if the required reaction components are continuously fed into and discharged from unit b.

Two forms of apparatus constructed in accordance with the invention will now be described in greater detail by way of example only, with reference to the accompanying drawings, of which Figures 1 and 2 are diagrammatic longitudinal sections through the apparatus. Referring now to Figure 1, fibres which may, for example, be in the form of flocks (10) are fed into a pretreating unit, e.g., a hopper feeder (1) wherein the flocks are opened up several times; via a conveyor belt (9) the fibres are then fed into unit b, particularly a sieve drum washer (2) which is filled and refilled with the reaction mixture via a feed line (13) connecting it with unit a, e.g., a tank (6) equipped with an agitator (8).The fibres which are moistened with an ample quantity of the reaction mixture are freed again from parts of the reaction mixture in unit c, e.g., a padder (3), leaving at least the quantity required for reaction. Following the squeezing operation in unit c the squeezed off fibres are loosened again in a post-treating device, e.g., an unravelling machine (4), in order to facilitate the subsequent reaction. The fibres containing the remainder of the aqueous alkaline reaction mixture are fed via a conveyor belt (14) into unit d, particularly a sieve drum drier (5), wherein they are treated with hot air.

The apparatus of Figure 2 is similar to that shown in Figure 1, except that unit d is a sieve belt steamer (7), wherein the fibres, while being transported over a sieve belt (15), are treated with hot or superheated steam produced from water contained in unit (12) with the aid of heating coils; this sieve belt drier may also be equipped with additional heating coils (11) arranged at the top. The fibres discharged from unit d in either embodiment have been crosslinked and etherified to the abovespecified extent and have, thus, become swellable.

If the cellulosic starting material is not in the form of fibres, but e.g., in the form of a woven fabric, a non-woven fabric, a blended woven fabric, a blended non-woven fabric, a sponge cloth, or a film, the devices 1 and 4 are not required in the apparatus of the invention, as it is unnecessary or impossible to open up or loosen these starting materials.

The process and the apparatus of the invention enable a technologically simple preparation of the products, since there is, for example, no need for explosion-proof equipment parts. In addition, the reaction time may be reduced, because the process allows a combination of alkalizing, etherifying and crosslinking in one reaction step. By contacting the fibres or sheet materials with considerabie quantities of the reaction mixture a good reaction behaviour is ensured; the actual chemical reaction is then carried out with the required quantity of the reaction mixture only. Among other advantages, it is possible to save energy and to use equipment which is not excessively large.

The fibres or sheet materials prepared, according to the process of the invention are, especially, used in the production of nonwoven fabrics. The other afore-mentioned applications are, however, also feasible. Further details with respect to the incorporation of, particularly, swellable fibres in nonwoven fabrics or sheet materials having a basis of polymer compositions are disclosed in the following publications: German Offenlegungsschriften Nos 2,756,671 (incorporation in polyurethane), 2,756,484 (incorporation in polyvinyl chloride), 2,710,874 (incorporation in nonwoven fabrics), 2,736,205 (incorporation in rubber), and 2,736,147 (incorporation in adhesives).

The parameters used in the description and in the examples to characterise the carboxyalkylcelluloses prepared according to the invention are defined as follows: WRV Water retention value of the sweliable crosslinked polymer in % by weight, measured against 1,600 times the acceleration due to gravity, relative to its water-insoluble fraction; WRV is determined after immersing the sample in water.

WUA Water-insoluble fraction in the swellable crosslinked polymer.

DS Degree of substitution, i.e. the average number of substituted hydroxyl groups on the anhydro-D-glucose units, from 0.0 to 3.0.

SOH20 Absorption capacity of the products prepared in the process for H20 in % by weight, relative to their total weight; SVH2o is determined after H20 has been absorbed by the sample up to saturation.

The following Examples 1 to 12 and 1 4 to 23 illustrate the invention; Example 1 3 is for comparison.

Example 1 40 g of rayon staple fibres (1.7 dtex, length 40 mm) are immersed during 5 minutes at room temperature in a solution composed of 92.7 g of NaOH, 270 g of Na-monochloroacetate, 11.46 g of bisacrylamido-acetic acid, and 626 g of H20, and are then treated in a centrifuge to yield a reaction weight (fibre+reaction mixture) of 125 g. To effect the actual chemical reaction (alkalising, etherifying, and crosslinking), the mixture is stored during 30 minutes in a drying chamber heated to 800 C. After neutralising with hydrochloric acid the reaction product is filtered, and the solid residue is washed free from salt in a 70% by weight aqueous methanol. The fibre material dried at a temperature of about 600C has the following parameters: WRV=1,560, WUA=69, and DS=0.29.

Example 2 The procedure is the same as in Example 1, but in this case 22 g of the fibres are immersed in a solution composed of 60 g of NaOH, 1 75 g of Na-monochloroacetate, 5.94 g of bisacrylamido-acetic acid, and 459 g of H2O; the fibres are centrifuged to a reaction weight of 75.7 g. The reaction time is 60 minutes at a temperature of 800 C. The fibre material has the following parameters: WRV=4,770, WUA=58, and DS=0.36.

Example 3 The procedure is the same as in Example 2, but the reaction time is 1 5 minutes at a temperature of 120cm. The fibre material has the following parameters: WRV=4,830, WUA=62, and DS=0.34.

Example 4 The procedure is the same as in Example 1, but the reaction time is 10 minutes at a temperature of 600C. The fibre material has the following parameters: WRV=4,680, WUA=60, and DS=0.33.

Example 5 The procedure is the same as in Example 1, but in this case chemical reaction is carried out during 30 seconds in a microwave oven manufactured by Linde ( Microtherm LMG 701). The fibre material has the following parameters: WRV=10,350, WUA=57, and yes=0.29.

Example 6 The procedure is the same as in Example 1, but in this case 25 g of the fibres are immersed in a solution composed of 49 g of NaOH, 72 g of Na-monochloroacetate, 2.44 g of bisacrylamido-acetic acid and 189 g of H2O; the fibres are centrifuged to a reaction weight of 98.6 g. Chemical reaction is carried out on a sieve netting, using a stream of hot air at a temperature of 1300 C, which is caused to act during 4 minutes. The fibre material has the following parameters: WRV=5,1 50, WUA=59, and DS=0.49.

Example 7 The procedure is the same as in Example 1, but in this case 20 g of the fibres are immersed in a solution composed of 52 g of NaOH, 89.98 g of acrylamide, 6.44 g of bisacrylamido-acetic acid, and 352 g of H2O; the fibres are centrifuged to a reaction weight of 91 g. The reaction time is 1 5 minutes at a temperature of 1200 C. The fibre material has the following parameters: WRV=12,260 and WUA=44.

Example 8 The procedure is the same as in Example 7, but the reaction time is 45 seconds in the microwave oven of Example 5. The fibre material has the following parameters: WRV=7,800 and WUA=56.

Example 9 The procedure is the same as in Example 7, but in this case 20 g of the fibres are immersed in a solution composed of 52.7 g NaOH, 91.2 g of acrylamide, 6.5 g of bisacrylamido-acetic acid, and 356 g of H2O; the fibres are centrifuged to a reaction weight of 84.7 g. The fibre material has the following parameters: WRV=1 2,470 and WUA=24.9.

Example 10 The procedure is the same as in Example 9, but chemical reaction is carried out during 45 seconds in the microwave oven. The fibre material has the following parameters: WRV=2,670 and WUA=60.2.

Example 11 2.5 kg of rayon staple fibres (1.7 dtex, length 40 mm) are immersed during 10 minutes at room temperature in a solution composed of 5.3 kg of a 50% strength aqueous NaOH solution 7.74 kg of Na-monochloroacetate, 0.263 kg of bisacrylamido-acetic acid and 1 8 kg of H2O, and are then treated in a centrifuge to yieid a reaction weight of 10.135 kg. To effect the actual chemical reaction the mixture is filled into a polyethylene bag and stored for 60 minutes in a return-air drying chamber heated to 700C. After neutralising with glacial acetic acid the reaction product is filtered and the solid residue is washed free from salt in an extraction column using an 80% by weight methanol. The fibre material which is dried at about 600C has the following parameters: WRV=1,170, WUA=77, and DS=0.45.

Example 12 The procedure is the same as in Example 11, but in this case a solution is used which is composed of 5.633 kg of a 50% strength aqueous NaOH solution, 6.566 kg of Na-monochloroacetate, 0.279 kg of bisacrylamido-acetic acid, and 18.77 kg of H20; the fibres are centrifuged to a reaction weight of 7.8 kg. The fibre material has the following parameters: WRV=3,270, WUA=74, and DS=0.31.

Example 13 The procedure is the same as in Example 12, but chemical reaction is carried out during 26 hours at room temperature (230C). The parameters of the fibre material are indicative of a still incomplete reaction: WRV=420, WUA=86, and DS=0.16.

Example 14 7.6 g of a nonwoven fabric consisting of 50% polyester fibres and 50% rayon staple fibres are immersed during 5 minutes at room temperature in a solution'composed of 92.6 g of NaOH, 270 g of Na-monochloroacetate, 11.5 g of bisacrylamido-acetic acid, and 776 g of H2O and are then squeezed off to a reaction weight of 1 4.7 g. To effect the actual chemical reaction the mixture is stored during 1 5 minutes in the drying chamber heated to about 1 300C. After neutralising with glacial acetic acid the reaction product is filtered, and the solid residue is washed in a 70% by weight aqueous isopropanol.

After this treatment the dried nonwoven fabric has an absorption capacity for water of 2,680% by weight, as compared to 888% by weight prior to the treatment. The absorption capacity of the nonwoven fabric is determined after applying H2O to the sample up to saturation; it is related to the total weight of the nonwoven fabric.

The following table gives the moiar relationships for the participants in the reactions of Examples 1 to 1 3, as present in the materials squeezed off to reaction weight.

Number of moles of reaction component:

cellulose Na-monochloro- 4 crosslinking Example hydrate NaOH H20 acetate acrylamide agent 1 1 085 12,/ U,tS 2 1 0,90 15,3 0,90 - 0,02 3 1 0,85 12,7 0,85 - 0,02 4 1 0,85 12,7 0,85 - 0,02 5 1 0,85 12,7 0,85 - 0,02 6 1 1,98 17,0 1,00 - 0,02 7 1 1,59 23,8 - 1,55 0,04 8 1 1,59 23,8 - 1,55 0,04 9 1 1,92 - 28,8 - 1,87 0,04 10 1 1,92 28,8 - 1,87 0,04 11 1 1,12 16,8 1,12 - 0,02 12 1 1,00 17,0 0,80 - 0,02 13 1 1 1,00 17,0 0,80 - 0,02 Example 15 1 5 g of a blended woven fabric consisting of 50% polyester fibres and 50% cotton are immersed during 5 minutes at room temperature in a solution composed of 92.6 g of NaOH, 270 g of Na monochloroacetate, 11.5 g of bisacrylamido-acetic acid, and 776 g of H2O and are then squeezed off to a reaction weight (woven fabric+reaction mixture) of 32.7 g. To effect the actual chemical reaction (alkalizing, etherifying, and crosslinking) the mixture is stored during 1 5 minutes in the drying chamber heated to about 1 200C. After neutralising with glacial acetic acid the reaction product is filtered and the solid residue is washed in a 70% by weight strength isopropanol; after this treatment the dried woven fabric has a SVH2O of 598, as compared to 1 83 prior to the treatment.

Example 16 20 g of a linen fabric are treated as in Example 1 5, but are squeezed off to a reaction weight of 48.5 g. After this treatment the dried fabric has a SVH2O of 530, as compared to 205 prior to the treatment.

Example 17 10 g of a nonwoven-based paper having a weight per unit area of 25 g/m2 are treated as described in Example 15, but are squeezed off to a reaction weight of 25 g. After this treatment the dried paper has a SVH2O of 470, as compared to 240 prior to the treatment.

Example 18 The required reaction mixture is prepared as follows: 42.5 kg of NaOH are added to 325 kg of H2O while stirring, and when the aqueous NaOH solution has cooled down, first 10.5 kg of bisacrylamido-acetic acid and then 123 kg of Na-monochloroacetate are added. Rayon staple fibres (1.7 dtex, length 40 mm) which have been opened up three times in the hopper feeder are added to this reaction mixture in the sieve drum washer, and the fibres saturated with the reaction mixture are then squeezed off in the padder in such a way that 100 g of untreated fibres weigh 300 g prior to carrying out the actual chemical reaction, i.e. 1 00 g of the fibre material contain 200 g of the reaction mixture.After the fibre material has again been opened up in an unravelling machine, it is passed through a sieve drum drier where the actual chemical reaction takes place; the temperature in the drier is 1 050C, and the fibres stay in the drier for 2.75 minutes. Following neutralising in glacial acetic acid and washing the reaction product in water and a 100% strength isopropanol, the fibre material may, if desired, be conditioned, for example, using the 0.3% strength conditioning agent (!)Leomin HSG (a fatty acid polyglycol ester) manufactured by HOECHST AG. The dried fibres have the following parameters: WRV=500, WUA=93, and DS=0.2.

Example 19 The procedure is the same as in Example 18, but chemical reaction is carried out in a sieve belt steamer; the temperature in the steamer is 1 000C; the fibres stay in the steamer for 3 minutes. The dried fibres have the following parameters: WRV=600, WUA=92.5, and DS=0.21.

Example 20 The procedure is the same as in Example 15, but the reaction mixture does only contain 4.2 kg of bisacrylamido-acetic acid, and the fibres are squeezed off in such a way that 100 g of the untreated fibre material contain 1 70 g of the reaction mixture. The reaction is carried out in the sieve drum drier at 950C and during a stay of the fibres in the drier of 1.5 minutes. After neutralising in glacial acetic acid, washing the reaction product in a 70% strength aqueous isopropanol, and drying, the fibres have the following parameters: WRV=3,277, WUA=51, and DS=0.43.

Example 21 A sponge cloth prepared from cellulose hydrate (weight per unit area 250 g/m2) is reeled off from a roll directly into the sieve drum washer and is treated according to Example 20; squeezing off is done in such a way that 100 g of the untreated sponge cloth contain 220 g of the reaction mixture. The saturated and then squeezed off sponge cloth is not opened up, but is directly fed into the sieve drum drier and reacted at 950C during 1.5 minutes. After neutralising in glacial acetic acid, washing in a 70% strength aqueous isopropanol, and drying, the sponge cloth has the following parameters: WRV=580 (untreated sponge cloth: 102), WUA=84.5, and DS=0.28.

Example 22 The procedure is the same as in Example 20, but in this case a defibrillised pine sulphite pulp is used as the starting material and squeezing off is done is such a way that 100 g of pulp contain 200 g of the reaction mixture. By means of the unravelling machine a uniform, about 1 cm thick layer is fed into the sieve drum drier and caused to react at 950C during 2 minutes. The dried pulp has the following parameters: WRV=408, WUA=80.8, and DS=0.26.

Example 23 The procedure is the same as in Example 20, but in this case a cotton fabric is used as the starting materials which is not opened up. The reaction is carried out in the sieve drum drier at 950C during 2 minutes. The dried fabric has the following parameters: WRV=350 (untreated fabric: 90), WUA=95, and DS=0.18.

Claims (21)

Claims

1. A process for the manufacture of a swellable crosslinked carboxyalkylcellulose which comprises treating a shaped structure or structures comprising cellulose hydrate or natural cellulose with a carboxyalkylating etherifying agent and a crosslinking agent in an aqueous alkaline medium, the quantity of the medium and the reactants contained therein being greater than required for reaction with the cellulose or cellulose hydrate, removing part of the medium, while leaving sufficient for the reaction, and heating the cellulose or cellulose hydrate and the remaining reaction mixture.

2. A process as claimed in claim 1, wherein the shaped structure is or shaped structures are fibres, textile sheet material containing fibres, or sheet material of other kinds, based on cellulose hydrate or natural cellulose.

3. A process as claimed in claim 1 or claim 2, wherein the etherification carried out is a carboxymethylation with monochloro-acetic acid or the salts thereof.

4. A process as claimed in any one of claims 1 to 3, wherein the crosslinking carried out is a reaction with phosphorus oxychloride, acrylamidomethylene-chloroacetamide or with a compound which carries at least one of the following functional groups: the acrylamido group, R, being H or CH3

an a halogenoepoxy group, Hal being Cl or Br

the chloroazomethine group

the allyloxy azomethine group N=COCH2-CH=CH2

5. A process as claimed in claim 4, wherein crosslinking is effected using 0.0005 to 0.2 part by weight of the crosslinking agent, relative to 1 part by weight of the natural cellulose or of the cellulose hydrate.

6. A process as claimed in any one of claims 1 to 3, wherein crosslinking is effected using at least 0.01 part by weight of dichloro-acetic acid, relative to 1 part by weight of the natural cellulose or of the cellulose hydrate.

7. A process as claimed in any one of claims 1 to 6, wherein the natural cellulose or cellulose hydrate is brought into contact with the aqueous alkaline reaction medium by means of spraying or immersing.

8. A process as claimed in any one of claims 1 to 7, wherein the surplus quantity of the reaction medium is removed from the cellulose hydrate or natural cellulose by squeezing off or centrifuging.

9. A process as claimed in any one of claims 1 to 8, wherein heat is applied in the form of hot air or steam or by a treatment with microwaves.

10. A process as claimed in any one of claims 1 to 9, wherein fibres are treated, and they are cellulose hydrate fibres which have lengths ranging from 30 mm to 1 50 mm, particularly from 30 mm to 60 mm.

11. A process as claimed in any one of claims 1 to 10, wherein sheet materials are treated, and they are films or sponge cloths composed of cellulose hydrate.

1 2. A process as claimed in claim 1, carried out substantially as described in any one of Examples 1 to 12 or 14 to 23.

1 3. A process as claimed in claim 1, carried out in an apparatus substantially as described herein with reference to and as illustrated by either of the accompanying drawings.

14. A swellable crosslinked carboxyalkylcellulose made by a process as claimed in any one of claims 1 to 13.

1 5. Apparatus for carrying out a process for preparing swellable crosslinked carboxyalkylcelluloses by reacting cellulose, a carboxyalkylating etherifying agent, and a crosslinking agent in an aqueous alkaline medium, comprising a) a unit for preparing and storing the reactant-containing aqueous alkaline reaction medium, b) a unit for contacting fibres, textile sheet materials containing these fibres, or sheet materials of other kinds, having a basis of cellulose hydrate or natural cellulose, with an ample quantity of the reactant-containing medium, c) a unit for removing the reaction n edium from the fibres or sheet materials contacted therewith, so that at least the quantity required for reaction is still present, d) a unit for treating with heat energy the fibres or sheet materials containing the remainder of the aqueous alkaline reaction mixture, and connecting elements between units a to d.

1 6. Apparatus as claimed in claim 15, wherein unit b is preceded by a device for pretreating unreacted natural cellulose in the form of fibres or unreacted cellulose hydrate in the form of fibres.

1 7. Apparatus as claimed in claim 1 5 or claim 16, wherein between units c and d a device is provided for post-treating fibres of natural cellulose or of cellulose hydrate which contain the remainder of the aqueous alkaline reaction mixture.

18. Apparatus as claimed in any one of claims 1 to 17, wherein unit b is a sieve drum washer and unit d is a sieve drum drier or a sieve belt steamer.

1 9. Apparatus as claimed in claim 15, substantially as described with reference to and as illustrated by the accompanying drawings.

20. Apparatus as claimed in any one of claims 1 5 to 19, which contains the reactant-containing medium and the cellulose or cellulose hydrate.

21. A non-woven fabric comprising a fibre or sheet material made by a process as claimed in any one of claims 1 to 13, or in an apparatus as claimed in any one of claims 15 to 20.